Standing seam metal roofs are formed from a plurality of interconnected panels supported by purlins, or joists. The standing seams are constructed from interconnected roof panels. In the prior art, hold-down clips are interleaved between the abutting adjacent panels. The standing seams are difficult to seal against moisture. The sealing problem is exacerbated by the necessity that the roof panels be permitted to expand and contract in accordance with the temperature variations to which they are subjected. The stresses and strains introduced by the expansion and contraction of the roof panels has been alleviated, in the prior art, by providing clips with a sliding connection between the base secured to a purlin and the hold-down portion connected to a standing seam.
We have found that the problem is not completely solved by allowing thermal expansion and contraction of the panels, since clips of the prior art allow equal amounts of movement for expansion and contraction. The ambit of movement is limited by stops. These stops are carried by the base, which is attached to a purlin or the like. They are necessary to prevent the upper and lower parts from becoming free from each other. Since each standing seam panel is advantageously fixed only at its lowest point into a wall, sliding clips of the prior art allow the panel to move at all other points. Thus, when the temperature rises, the interconnected metal panels will expand and move uphill. The clip farthest from the fixed low end will move the farthest distance. If at a given temperature this distance is equal to the maximum possible movement permitted by the clip, a further increase in temperature will cause the panel to be subjected to compression. One of a number of things will then occur. A clip, or clips, may be destroyed; the fastening means at the low end of the panel may break; the low end of the panel itself may rupture; or the metal panel will buckle slightly. The slight buckling, necessary to relieve the compression, is transient and will not affect the performance of the roofing. The buckling of the panels acts as a safety valve and causes no permanent damage to the roofing system. If, on the other hand, the temperature drops, the panel will contract and move downhill. Again, at a given temperature, at some point, the maximum movement of the clip farthest from the low end of the panel is reached. If sufficient ambit of movement is not allowed, a further decrease in temperature will then cause the panel to be placed in tension. Since the panel is contracting, the result will be that one or more of the fasteners at the low end or the clip at the high end, or the panel itself at the low end, will fail.
We have found that a better standing seam roof can be constructed if the clip allows more contraction than expansion before encountering a stop, rather than allowing equal amounts of movement as is now done in the prior art. It should be noted that some manufacturers fix the panel at a place other than at the end. The result, however, is the same, no matter where the point of fixation is placed. There is always a fixed point and a floating point.